Exercise turns bad fat to good in study

Exercise can turn bad white fat into its healthier, calorie-burning brown version and may help keep diabetes at bay, according to research.

Men who trained for 12 weeks on an exercise bicycle showed a browning of their subcutaneous white adipose tissue in a study presented at the American Diabetes Association meeting. In a separate study in mice, brown fat was linked with better glucose tolerance and insulin sensitivity, suggesting the substance may play a role in preventing diabetes.

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The results build on earlier studies showing brown fat, previously thought to be active only in babies and children, contains calorie-burning properties and may help protect against age-related weight gain. The study also suggests that exercise is beneficial even if it doesn't result in weight loss, researchers said.

"Our results showed that exercise doesn't just have beneficial effects on muscle, it also affects fat," Kristin Stanford, a postdoctoral fellow at Joslin Diabetes Center in Lanham, Maryland, said in a statement. "It's clear that when fat gets trained, it becomes browner and more metabolically active. We think there are factors being released into the bloodstream from the healthier fat that are working on other tissues."

To determine brown fat's metabolic effects, researchers transplanted fat from mice that ran on an exercise wheel for 11 days into sedentary, high-fat mice, and saw improvements that lasted for at least 12 weeks. The fat that was more brown was associated with better body composition, a reduction in fat mass and improved insulin sensitivity and glucose uptake in mice. Those effects in humans weren't determined.

The studies were funded by the American Diabetes Association and the National Institutes of Health. The trial in humans comprised 10 healthy men.

"Our work provides greater motivation than ever to get out there and exercise," Stanford said.

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